The present invention relates to control systems for operating robots and workcell devices in robotic workcells and more particularly to the implementation of input/output signal interfacing in such control systems.
In a typical factory workcell, one or more robots are operated with various workcell devices to perform predetermined work operations on materials and/or products being processed in the workcell. Generally, the robots and workcell devices are cooperatively operated so that the materials or products are moved from device to device or from device to robot or vice versa and so that specified device or robot work operations are performed on the materials or products. The work area and its layout depend on what is being processed or made in the work cell, what devices and robots are provided and how such devices and robots are operated and interacted.
To operate a workcell as described, it is necessary that various workcell signals be generated for input to the control system and that the control system generate output signals for the purposes of monitoring and controlling the operation of the workcell robot(s) and devices. Varying levels of complexity may be involved in the local control of the various workcell devices.
One conventional approach for configuring a workcell control system with input/output signal interfacing simply involves the use of a robot controller to which robot and other workcell device signals are applied as inputs for programmed logic processing from which output monitoring and control signals are generated for the workcell. With this approach, the control loading created by the need for sequential logic control and local control of the workcell devices places restraints on the capacity of the robot controller to provide real time robot arm control. Further, this robot controller centered configuration is highly inflexible to modification after installation or for installation in different applications, especially since it requires the connection of hard wires between the robot controller and the various input/output signal locations. The robot controller centered configuration becomes increasingly disadvantageous as work area size and/or control complexity increases.
Another approach to workcell control configuration, and perhaps the most prevalent one, involves the use of one or more programmable logic controllers (PLCs). In the robot controller/PLC configuration, the PLC is placed at a predetermined workcell location and workcell input/output connections and robot connections are made to the PLC. Local workcell device control and workcell sequential logic control can be performed by the PLC independently of the robot controller yet robot and workcell device control can be performed interdependently because of the coupling of the PLC and the robot controller. As a result, the full capacity of the robot controller is essentially made available for robot arm control.
Nonetheless, the robot controller/PLC configuration has disadvantages including:
1. The hard wiring requirements from the PLC to the various signal locations can be extensive, i.e. increasing with work area size and control system complexity.
2. PLCs are relatively expensive especially for applications having relatively low control complexity.
3. The PLC is separately programmed, and a programming language different from the robot controller programming language normally must be used for PLC programming. Therefore, two or more skilled people are normally required for system programming and for workcell operation.
There accordingly has been a need for development of a robotic workcell control system in which better, more efficient and less costly input/output interfacing is provided so that improved workcell operations can be achieved. The present invention is directed to this end.